Sulphur-isotopic composition of the deep-sea mussel Bathymodiolus marisindicus from currently active hydrothermal vents in the Indian Ocean

Sulphur-isotopic composition of soft tissues from bathymodiolus marisindicus collected from hydrothermal vents in the indian ocean was reported. the [delta]34s values of the soft tissues (+3[similar]+5‰ vs cañyon diablo troilite) were nearly identical to those from the associated hydrothermal fluid and chimney sulphides (+5 to +8‰), but were significantly different from that of the common seawater sulphate (+21‰), which suggested that the endosymbiotic bacteria used sulphide in the fluid as an energy source. transmission electron microscopic observation of the endosymbionts also suggested that the symbiont is a thioautotroph. bathymodiolus species, which depend on either sulphide or methane oxidation, or both, have a worldwide distribution. bathymodiolus marisindicus from the indian ocean has a close relationship with congeners in the pacific ocean as evidenced by form of symbiosis. biogeography and migration of the genus bathymodiolus based on the relevant data are briefly discussed.</p

Low sulfur isotopic signatures (δ^<34>S) of macrozoobenthos from a brackish lagoon: contribution of microbially reduced sulfides

Stable sulfur isotope ratios (δ^S) of infaunal bivalves (Macoma contabulata, Nuttallia olivacea, and Ruditapes philippinarum) and polychaetes (Hediste spp.; consisted of H. atoka and H. diadroma) collected from two stations in the Gamo Lagoon (Japan) were determined to assess trophic pathways in highly reductive, estuarine soft-bottom habitats. The stations were characterized by distinctive sediment characteristics (Station A, sandy sediment with low sulfide content; Station B, muddy and sulfide-rich sediment). Soft tissues of the consumers exhibited much more depleted δ^S values (+3.2 to +12.1‰) than those of dissolved sulfate in the water column (+20.6 to +20.8‰). The value for each species was 1.6 to 5.3‰ lower at Station B than at Station A. These results suggest the assimilation of sulfides in the sediment (δ^S; -23.2 to -22.7‰) via microbial trophic pathways. In this lagoon, benthic microalgae and/or other microbes in the sediment are the most probable ^S-depleted food source for the consumers. Interspecies variations in δ^S values are explained by the different dietary contribution of the ^S-depleted diets versus ^S-enriched phytoplankton and are closely related to different feeding habits (i.e., surface-deposit feeding, facultative suspension feeding, and obligatory suspension feeding).論文Articl

Spatial shifts in food sources for macrozoobenthos in an estuarine ecosystem: carbon and nitrogen stable isotopes.

Abstract Carbon and nitrogen stable isotope (d 13 C and d 15 N, respectively) analyses were made on estuarine macrozoobenthos in order to examine the relationships between their feeding habits (feeding mode and food selectivity) and the spatial shifts in food sources from upstream to downstream in an estuary. The d 13 C values of two ocypodid crabs were similar to those of benthic diatoms, indicating that they use their specialized mouth parts to selectively feed on benthic diatoms. The d 13 C values of a gastropod and another ocypodid crab at the site furthest downstream were higher than values at an upstream site, suggesting that these unselective deposit feeders shift from feeding mainly on benthic diatoms downstream to feeding on sediment organic matter (SOM) upstream. The d 13 C values of deposit feeding polychaetes were not significantly different among sampling sites, indicating that they feed mainly on SOM at all sites. These results show that species-and site-specific feeding habits must be considered when evaluating the roles of macrozoobenthos in regulating estuarine material flows

Sclerite formation in the hydrothermal-vent “scaly-foot” gastropod — possible control of iron sulfide biomineralization by the animal

A gastropod from a deep-sea hydrothermal field at the Rodriguez triple junction, Indian Ocean, has scale-shaped structures, called sclerites, mineralized with iron sulfides on its foot. No other organisms are known to produce a skeleton consisting of iron sulfides. To investigate whether iron sulfide mineralization is mediated by the gastropod for the function of the sclerites, we performed a detailed physical and chemical characterization. Nanostructural characterization of the iron sulfide sclerites reveals that the iron sulfide minerals pyrite (FeS2) and greigite (Fe3S4) form with unique crystal habits inside and outside of the organic matrix, respectively. The magnetic properties of the sclerites, which are mostly consistent with those predicted from their nanostructual features, are not optimized for magnetoreception and instead support use of the magnetic minerals as structural elements. The mechanical performance of the sclerites is superior to that of other biominerals used in the vent environment for predation as well as protection from predation. These characteristics, as well as the co-occurrence of brachyuran crabs, support the inference that the mineralization of iron sulfides might be controlled by the gastropod to harden the sclerites for protection from predators. Sulfur and iron isotopic analyses indicate that sulfur and iron in the sclerites originate from hydrothermal fluids rather than from bacterial metabolites, and that iron supply is unlikely to be regulated by the gastropod for iron sulfide mineralization. We propose that the gastropod may control iron sulfide mineralization by modulating the internal concentrations of reduced sulfur compounds